Soon you will have forgotten all things: soon all things will have forgotten you.
It is human nature to love even those who trip and fall. This follows if you reflect at the time that all men are brothers; that they go wrong through ignorance, not intent; that in a short while both you and they will be dead; and, above all, that the man has not harmed you - he has not made your directing mind worse than it was before.
Universal nature uses the substance of the universe like wax, making now the model of a horse, then melting it down and using its material for a tree; next for a man; next for something else. Each one of these subsists for only the briefest time. It is no more hardship for a box to be broken up than to be put together.
The first passage makes your brain freeze up with the double-negative. Basically, Marcus is saying his main worry in life is living and acting rationally and socially.
Next, yet another reminder that you, me, your friends, your family - we all die (you will forget everything) and not only will we all die, but hardly anyone, if anyone at all, will know who we were. Such is the vastness of time and space.
The next passage is one I particularly love. Briefly stated, Marcus is reminding himself to give others the benefit of the doubt. We all trip and fall and we can easily forgive others who make mistakes. Generally speaking, there is no hateful or negative intent when people make mistakes. Even if there were, I'm sure we can find space in our heart to forgive and forget. And most importantly, if someone "trips and falls" and whether or not they intended harm or not, ultimately your directing mind was not harmed by this action.
The last passage is one Marcus has discussed before. We see all around us, the product of the Universe. From the Universe springs life. The life grows, matures and dies and the material from which it was made, decomposes and becomes the material for new life. All this material is nothing but wax or clay molded into a form and then dissolved and molded into something new; and this repeats endlessly. Two lessons can be learned here: 1) our life is short 2) we can be like the Universe and whatever material has been given you, mold it into something beautiful (akin to the saying, 'when life gives you lemons, make lemonade!)
(see also Citadel p. 29, 38-40, 166, 176, 229, 259, 268)